1. Field of the Invention
The present invention generally relates to a method of detecting a drift amount in scanning a form slide film of an optical information recording apparatus in which data information of the form slide is optically scanned by on two-dimensional scanning beam to be optically recorded on a recording medium by way of the raster scanning. More particularly, the present invention is directed to a method of detecting the drift amount occurring when the frame-information stored position of the form slide film is optically scanned with respect to the data stored position thereof and to an apparatus for detecting such a drift amount.
2. Description of the Prior Art
As such an information recording apparatus, a computer output microfilm apparatus (referred to as "laser-COM" hereinafter) is known, in which print data (variable information) supplied from the computer and desirable form data (fixed information) are recorded on microforms by employing a laser beam as scanning light.
An optical scanning system of the above-described laser-COM will now be summarized with reference to FIG. 1.
An argon (Ar) laser 1 emits blue green light beams for recording purposes, which are indicated by "B". The blue green light beams B are intensity-modulated in an optical modulator 2 by video signals (will be discussed later) and thereafter pass through a first dichroic mirror 3. A helium-neon (He - Ne) laser 4 emits red light beams for reading purposes, which are denoted by "R". The red light beams R are incident upon a first reflecting mirror 5 and reflected therein and thereafter incident on the first dichroic mirror 3. The red light beams R are reflected on the first dichroic mirror 3 and mixed with the other light beams for recording purposes that have passed through this dichroic mirror 3. The combined light beams are incident on a rotating polyhedric mirror 7 through a second reflecting mirror 6. In this case, the first dichroic mirror 3 is designed to pass the blue and green light beams therethrough and to reflect the red light beams thereon.
The rotating polyhedric mirror 7 is rotated in a predetermined direction at a constant rate by a motor 9 to which a power is supplied from a motor drive circuit 8. As a result, the combined light beams R, B incident upon the respective mirror surface of the rotating polyhedric mirror 7 are reflected on these mirror surfaces and simultaneously deflected (referred to as "horizontal-deflected beams"). Then, the mixed light beams are converted into primary scanning light having a repetition period that is defined by the beam reflections occur in the respective mirror surfaces of the rotating polyhedric mirror 7. The primary scanning light is incident upon a second dichroic mirror 11 via a convergent optical system 10. The second dichroic mirror has such characteristics that the recording blue-green light beams and the reading red light beams can be transmitted therethrough and a part of the reading red light beams can be reflected thereon. Accordingly, in the mixed light beams incident upon the second dichroic mirror 11, both the blue-green light beams B and the red light beams R pass toward a galvanometer 12, and the red light beams R are partially reflected and incident upon a linear encoder 13.
In response to saw-tooth driving signals supplied from a galvanometer driver 14, the galvanometer 12 deflects the recording light beams R, B in a direction substantially perpendicular to the horizontal deflecting direction (referred to as "vertical deflection"). As described above, the galvanometer driver 14 produces the saw-tooth driving signals based upon clock signals derived from a clock signal generator 15 (will be discussed later). For instance, counting these clock signals in a vertical address signal generator 16 in the vertical deflection period enables the vertical address signals to be produced. In response to these address signals, the galvanometer driver 14 produces the above-described saw-tooth driving signals.
Since the blue green light beams and also the red light beams vertically deflected by the galvanometer 12 have been converted into the one dimensional scanning light by the rotating polyhedric mirror 7, they become two dimensional scanning light by means of such vertical deflections. Then, the two dimensional scanning light is incident upon a third dichroic mirror 17, thereby splitting it into the blue green light and the red light.
The two dimensional scanning light of the blue green light beams passing through the third dichroic mirror 17 is focused on recording materials such as films via a focusing optical system 18 to raster-scan them. The other two dimensional scanning light of the red light beams split by the third dichroic mirror 17 is incident upon a form slide film 20A via a third reflecting mirror 19.
In a form slide film device 20, a plurality of form slide films 20A, 20B, --- , 20N (N being number) are preset which are the most useable. Different slide images and writing frames constituted by a plurality of vertical and horizontal lines are recorded on these slide films 20A, 20B, --- , 20N. For the sake of simplicity, only two form slide films 20A and 20B are illustrated. One of these form slide films is selectively moved to a scanning position where it is scanned by the above two dimensional scanning light. As desired, the form slide films 20A, 20B, --- , 20N are arbitrarily detachable from the form slide device 20.
As seen from FIG. 1, the two dimensional scanning light R passes through the form slide film 20A and is converted in a first photomultiplier 21 to electric readout signals. The readout signals correspond to video signals of the writing frame image of the scanned form slide film 20A.
The red light beams R split by the second dichroic mirror 11 are, on the other hand, incident upon a linear encoder 13 to be one-dimensional-scanned. The linear encoder 13 is formed by a plurality of transparent and non-transparent line-shaped grids which are aligned parallel to the horizontal deflection direction and equidistantly separated to form a straight striped pattern. Pulsatory light obtained by scanning this linear encoder 13 by means of the horizontal deflection scanning light is converted by a second photomultiplier 22 into pulse signals as clock pulse signals. By applying these clock pulse signals to a phase-coupling type clock signal oscillator 23, clock signals are oscillated. The clock signals are used to synchronize the respective circuit elements of the laser-COM with each other under the desirable timings. The linear encoder 13, second photomultiplier 22, and clock signal oscillator 23 constitute a clock signal generating device 15.
Under the timing control of the clock signals derived from the clock signal generating device 15, character information corresponding to coded data from the character information source such as magnetic tapes etc. can be read out from a character generator 24 as video signals. These video signals derived from the character generator 24 are supplied to a signal composite circuit 25. While they form signals that are obtained by amplifying outputs of the first photomultiplier 21 in the amplifier 26 and thereafter shaping them in a level slicer 27 are supplied to the signal composite circuit 25, the above video signals are combined with the form signals in the signal composite circuit 25.
Thus the composite video signals are supplied through a modulator drive circuit 28 to the optical modulator 2 so as to intensity-modulate the recording light beams. As easily seen, the raster-scanned image projected toward the film F corresponds to an image formed by that the print data derived from the computer is written in a given position of the form frame selected by the form slide film.
Such an information recording apparatus is known from, e.g., U.S. Pat. Nos. 4,323,906 and 4,340,894.
In such a laser-COM apparatus, the film F is known as "a microform" in a roll type film or a sheet-like film. A microfiche is most favorably employed as the sheet-like microfilm. Both the data information referred to as "variable information" such as characters produced from the character generator 24 based on the data input of the computer (not shown in detail) and also the fixed information such as frame information of the form slide film 20A positioned in the reading path are recorded in turn on such a microform with one page per one frame. That is, the fixed information read out from the form slide film 20A corresponds to image information having a properly arranged layout of frames, explanation etc. When the form slide film 20A is substituted by another one, it is possible to select the proper fixed information for displaying the data on the frame etc. When the typical microfiche is used as the microform, the fixed information and the variable information are recorded in the following format. This format is constituted of a plurality of frames that are arranged in both the vertical and horizontal directions in a predetermined sequence.
In optically recording the information according to the format, the fixed information of the desirable form slide film 20A optically read out by the form slide device 20 and the variable information such as character data generated from the character generator 24 must be recorded on the film F without any positional misalignment. Then a drift amount of the vertical scanning for the form slide film 20A with respect to the optical center position of the vertical scanning beam is detected in the conventional laser-COM apparatus so that the position of the vertical scanning beam is shifted to a predetermined position, e.g., the optical center position of the form slide film 20A so as to eliminate the drift.
Referring now to the form slide film 20A as shown in FIG. 2, a description will be made of the conventional drift detecting method for the vertical scanning direction. As previously described, the form slide film 20A is set on the two-dimensionally scanned position of the form slide device 20, so that the desirable frame information and the form image can be two-dimensionally scanned by the above-described raster. The symbol "X" denotes the horizontal scanning direction and the symbol "Y" indicates the vertical scanning direction. A form image region 122 having a width "S" in the vertical scanning direction "Y" is drawn by a solid line, while a raster scanning region 123 defined by an area of the form slide film 20A having a width "V" in the vertical scanning direction is shown by a broken line. This region 123 also covers the frame image region 122. The raster scanning region 123 includes an adjustment or region having a width of "1.sub.o " because drift deviation of the raster scanning region 123 from the optical center "O" of the frame image region 122 can be adjusted by increasing or decreasing the number of the raster in the vertical direction, i.e., the vertical scanning pitch.
Elongate sensor marks 124, 125 and 126 for detecting the drift amount are intermittently formed in the right side out of the form image region 122 within the raster scanning region 123. As will be described hereinafter, when the raster intersects these sensor marks 124, 125 and 126, photoelectric conversion pulse signals are produced that corresponds to the number of the intersected rasters. These intersected rasters can be detected by way of the transmission mode or reflection mode. Thus, the number of the pulse signals corresponds to those of the raster intersecting the sensor marks.
The first-mentioned sensor mark 124 is formed in such a manner that one end of the sensor mark 124 is coincident with the scanning starting portion of the form image region 122 and a length thereof is denoted by "L.sub.1 ", i.e., the other end thereof does not reach a straight line "D" in the horizontal scanning direction. This straight line "D" intersects the scanning center "O". A length of the second sensor mark 125 is denoted by "L.sub.2 " which is relatively shorter than that of the first sensor mark 124. This second sensor mark 125 intersects the above straight line "D". One end of the second sensor mark 126 terminates the scanning end portion of the form image region 122 and this mark 126 extends in the straight line "D" but does not reach this line "D". A length of this mark 126 is indicated by "L.sub.3 ".
To detect a degree of the variation (i.e., an amount of the drift) on the relative position of the vertical scanning, when the form image is optically read from the form slide film 20A, the vertical address signal is compulsorily produced from the vertical address signal generator 16 so as to scan the optical center "O" of the form image region 122 by the straight line "D". This optical center "O" is determined by the optical components of the laser-COM apparatus. Accordingly, the galvanometer 12 can scan the position by receiving this vertical address signal, this position intersecting the optical center "O". From this center position, the vertical scanning commences so that the number of the pulse signals produced by intersecting the second sensor mark 125 is counted. If there is no drift in the scanning system and the first raster of the galvanometer 12 is coincident with the straight line "D" intersecting the optical center "O" upon receipt of the vertical address signal compulsorily produced from the vertical address signal generator 16, the number of the pulse signals produced by scanning a half length "L.sub. 2 /2" of the second sensor mark 125 is equal to a predetermined constant value. When the resultant pulse numbers are greater than this constant value, the raster scanning of the second sensor mark 125 is probably carried out from the upper position (viewed in FIG. 2) above the optical center "O" although the galvanometer 12 is compulsorily driven so as to scan the optical center "O". In other words, the total scanning length is greater than "L.sub.2 /2. Conversely, if the resultant pulse numbers are smaller than the constant values, the raster scanning of the second sensor marks 125 commences below the optical center "O" due to the above-described drift phenomenon. That is, these pulse numbers are always constant if there is no drift.
In accordance with the conventional drift detection, the drift amount of the optical system is detected by comparing the resultant pulse number to the predetermined reference value. The comparison result corresponds to the variation amount, i.e., the drift amount of the relative position between the form image region 122 of the form slide film 20A and the raster scanning region 123 in the vertical direction. As a result, this amount of the drift can be used as an amount of the drift correction so as to adjust the number of the raster scanning in the specific region "1.sub.o ", i.e., the vertical scanning pitch. This is effected by controlling the optical axis of the vertical scanning beam, i.e., the central position of the vertical deflection.
Since there is no direct relation of the first and third sensor marks 124 and 126 with regard to the present invention, no further description is made.
The conventional drift detection method owns the following drawbacks. That is, the drift corrections are performed for the succeeding form slide films by employing the drift amount that has been detected for the first frame of the form slide film only. Accordingly, if there is a variation in the drift amount of the galvanometer 12, or other optical components due to the temperature variation, this variation cannot be corrected for the succeeding film scanning and recording. In other words, once the drift detection is performed, no further drift correction is effected in the conventional drift detection method.
As is well known, a plenty of the film frames are usually recorded on the microfiche, so that each of the film frames must be recorded with an extremely high reduction ratio. If there is positional deviation between the form image data and the character information data, the overlapped portion of both the image data may be produced. Even if the drift amount is corrected with respect to the first form slide film, the overlapped image recording may occur in the conventional laser-COM apparatus since the temperature variation causes the optical scanning by the raster to be deviated from a predetermined center position.
It is an object of the present invention is to overcome the conventional drawbacks in the drift correction and to provide a continuous drift detection for the succeeding form slide films.
It is another object to provide a simple drift detecting method in the vertical scanning.
It is a still object to provide a precise drift detecting method in the vertical scanning.